Marine Glossary

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risk of collision

Collision risk is addressed in Rule 7. The un-stated implication is that collision risk exists if two approaching vessels would arrive at the same place at the same time if they continue on with their present speeds and courses. The Rule requires evaluation of this situation using compass bearings. This situation could exist, however, when the vessels are still separated by a great distance, large enough that in a practical sense there is no risk of collision yet. Hence when does the risk begin which triggers the actions required by the Rules?

This is not explicitly answered in the Rules, and even court cases involving collisions are very reluctant to assign a numerical distance to this separation. There are too many variable factors involved. Rather vague generalities have been proposed by several authors (based on court statements), the most common one repeated is that risk begins when the vessels are so close that a collision can indeed occur if either does not obey the Rules.

Certainly the separation calling for action is farther off than the realm of close-quarters. In other words, on deciding when to maneuver to keep clear of a crossing vessel on your starboard side, one should do so well before being exposed to risk from a sudden (illegal) turn to the left on their part... or the sudden (again illegal) tack of a sailing vessel you are passing.

Rule 17 requires the stand-on vessel to hold course and speed when risk exists, but the stand-on vessel is also given the right and even obligation to maneuver themselves to avoid collision if they deem the give-way vessel is not maneuvering in time. Clearly their own perception of close quarters enters their decision here. Consequently, the interpretation of "take early action" in Rule 16 must mean we should certainly maneuver well before the other vessel perceives we are entering their close quarters.

Keep in mind at all times, however, the catch-all Saving Grace of Rule 7a: If there is any doubt, the answer is yes. And if there is any further doubt about what to do, the answer is stop (Rule 8e).